Income Taxes (Income Tax Expense (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Successor
Income Tax Examination [Line Items]
Income tax provision (benefit) at statutory rate	$ 23,347		$ 54,843
Percentage depletion allowance	(7,708)		(20,439)
State taxes, net of effect of federal taxes	728		1,619
Change in valuation allowance	(19,118)		(39,336)
Other, net	1,108		2,829
Income Tax Expense (Benefit)	$ (1,643)		$ (484)
Predecessor
Income Tax Examination [Line Items]
Income tax provision (benefit) at statutory rate		$ (19,143)		$ (153,523)
Percentage depletion allowance		(11,041)		(30,799)
State taxes, net of effect of federal taxes		(2,195)		(9,256)
Change in valuation allowance		31,955		191,182
Other, net		(2,846)		(2,230)
Income Tax Expense (Benefit)		$ (3,270)		$ (4,626)